1. Field of the Invention
This invention relates generally to an apparatus and method for treating tinnitus, and in particular, to a human cerebral cortex neural prosthetic for delivering geometrically dispersed electrical signals to the patient""s primary auditory cortex and/or to a human cerebral cortex or the patient""s thalamus neural prosthetic for microinfusing geometrically dispersed portions of drugs to the patient""s primary auditory cortex or the patient""s thalamus.
2. Background of the Related Art
Tinnitus is a disorder where a patient experiences a sound sensation within the head (xe2x80x9ca ringing in the earsxe2x80x9d) in absence of an external stimulus. This uncontrollable ringing can be extremely uncomfortable and often results in severe disability. Tinnitus is a very common disorder affecting an estimated 15% of the U.S. population according to the National Institutes for Health, 1989 National Strategic Research Plan. Hence, approximately 9 million Americans have clinically significant tinnitus with 2 million of those being severely disabled by the disorder.
There are no treatments currently available that consistently eliminate tinnitus although many different types of treatments have been attempted. This wide variety of attempted treatments attests to the unsatisfactory state of current tinnitus therapy. Several more common attempts will discussed below.
One approach involves suppression of abnormal neural activity within the auditory nervous system with various anticonvulsant or local anesthetic medications. Examples of such anticonvulsant medications include Xylocaine and Lidocaine which are administered intravenously. In addition, since the clinical impact of tinnitus is significantly influenced by the patient""s psychological state, antidepressants, sedatives, biofeedback and counseling methods are also used. None of these methods has been shown to be consistently effective.
Another widely used approach to treating tinnitus involves xe2x80x9cmaskingxe2x80x9d undesirable sound perception by presenting alternative sounds to the patient using an external sound generator. In particular, an external sound generator is attached to the patient""s ear (similar to a hearing aid) and the generator outputs sounds into the patients ear. Although this approach has met with moderate success, it has several significant drawbacks. First, such an approach requires that the patient not be deaf in the ear which uses the external sound generator. That is, the external sound generator cannot effectively mask sounds to a deaf ear which subsequently developed tinnitus. Second, the external sound generator can be inconvenient to use and can actually result in loss of hearing acuity in healthy ears.
Yet another approach involves surgical resection of the auditory nerve itself. This more dangerous approach is usually only attempted if the patient suffers form large acoustic neuromas and tinnitus. In this situation, the auditory nerve is not resected for the specific purpose of elimination tinnitus but is removed as an almost inevitable complication of large tumor removal. In a wide series of patients with tinnitus who underwent this surgical procedure of acoustic nerve resection, only 40% were improved, 10% were improved and 50% were actually worse.
An alternative and somewhat more successful approach involves electrical stimulation of the cochlear. In patients who have tinnitus and have received a cochlear implant, as many as half reported some improvement in their tinnitus after implantation. Round window stimulation has also been useful in improving tinnitus in selected patients. However, the success rate of this approach has also remained relatively low.
Prior to the nineteenth century, physicians and scientists believed the brain was an organ with functional properties distributed equally through its mass. Localization of specific functions within subregions of the brain was first demonstrated in the 1800s, and provided the fundamental conceptual framework for all of modern neuroscience and neurosurgery. As it became clear that brain subregions served specific functions such as movement of the extremities, and touch sensation, it was also noted that direct electrical stimulation of the surface of these brain regions could cause partial reproduction of these functions.
It is therefore an object of the invention to provide a prosthetic apparatus which can be placed in one of a patient""s cerebral cortex or in the patient""s thalamus to reduce the effects of tinnitus.
Another object of the invention is to provide a prosthetic apparatus which can be positioned in the brain such that electric discharges can be accurately delivered to geometrically dispersed locations in either the cortex or thalamus.
Another object of the invention is to provide a prosthetic which allows a physician to physiologically test location and function of neural prosthetic electrodes to reduce or eliminate the patient""s tinnitus.
Another object of the invention is to provide a prosthetic apparatus which can be positioned in the brain such that microinfusions of a drug that reduces abnormal neural activity due to tinnitus can be administered in geometrically dispersed locations in the patient""s cortex or thalamus.
Another object of the invention is to provide a prosthetic apparatus which can support a reservoir of the drug so that the microinfusions can be continuously administered.
One advantage of the invention is that it reduces or eliminates the effects of tinnitus.
Another advantage of the invention is that it can utilize a single electrode.
Another advantage of the invention is that it can utilize a single catheter.
Another advantage of the invention is that it penetrates the brain as opposed to resting on the brain surface, thus requiring significantly less current to stimulate localized areas of the cortex or the thalamus.
Another advantage of the invention is that it penetrates the brain thus requiring significantly lower doses of the drug and hence reduces unwanted side effects related to inadvertent stimulation of surrounding tissue.
Another advantage of the invention is that the contacts are sufficiently closely arranged next to each other to provide high geometric resolution stimulation of the auditory cortex.
One feature of the invention is that it includes a penetrating longitudinal support or electrode.
Another feature of the invention is that it includes multiple contacts on the longitudinal support.
Another feature of the invention is that it includes a simulation device.
Another feature of the invention is that each contact can separately introduce electrical discharges in the primary auditory cortex.
Another feature of the invention is that it utilizes a catheter to administer micro-infusions of the drugs to disperse locations in the patient""s cortex or thalamus.
Another feature of the invention is that the catheter includes an electrode for recording discharges in the patient""s cortex or thalamus.
Another feature of the invention is that it utilizes a drug reservoir for containing reserve portions of the drug.
Another feature of the invention is that it can include a flexible wire multicontact electrode.
Another feature of the invention is that the flexible wire multicontact electrode is inserted into the brain using a rigid introducer.
Another feature of the invention is that a flat plastic plate attached to the longitudinal support (electrode) at the site of skull attachment and helps position the prosthetic in the auditory cortex. The flat plastic plate having a cup to receive a sphere coupled to leads which interconnect the contacts to the speech processor.
These and other objects, advantages and features of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.